1. Field of the Invention
The present invention relates to a digital/analog TV receiver which has a full-range scanning function for automatically identifying the transmission route of a broadcasting signal and automatically specifying the channel of the broadcasting signal as a receivable channel.
2. Description of the Related Art
The transmission route of television broadcasting signals is commonly classified into ground wave route and cable wave route. There are some TV receivers which can receive broadcasting signals from both the ground wave transmission route and the cable wave transmission route. When the frequency is different between the ground wave signal and the cable wave signal, the apparatus itself has to identify the transmission route of the broadcasting signal. Hence, a type of TV receiver is known which has a full-range scanning function for detecting the broadcasting signal received from a station, automatically identifying the transmission route of the broadcasting signal, and automatically specifying the channel of each receivable broadcasting signal.
The process of full-range scanning in the conventional TV receiver includes steps of examining alternately the presence of both ground wave and cable wave of the broadcasting signal throughout the full range of frequencies of the channels and determining from the result of the examination whether the broadcasting signal is received from the ground wave transmission route or the cable wave transmission route. After the transmission route of the broadcasting signal is determined, the presence of the broadcasting signal is examined throughout the frequencies to determine the receivable channels.
Meanwhile, a method of examining whether the broadcasting signal is a ground television broadcasting signal or a cable television signal is known including steps of examining the presence of broadcasting signals over a group of channels which are identical in the frequency and the channel number and determining from the result of the examination whether the broadcasting signal received by the receiver is a ground television broadcasting signal or a CATV signal (for example, as disclosed in Japanese Patent Laid-open Publication No. HEI 10-233970). Also, a method of specifying the channel of a received signal in a digital broadcast receiver is known where the number of PSK lock detecting actions for all the channels and the number of frame synchronization detecting actions for the channels in a particular frequency range are minimized for readily specifying the channel of a received signal in the range of broadcast frequencies (for example, as disclosed in Japanese Patent Laid-open Publication No. 2000-312134).
It is however needed for specifying the transmission route of a broadcasting signal through full-range scanning in any conventional broadcasting signal receiver to detect the presence of the broadcasting signal over two or more channels. Accordingly, the step of specifying the transmission route of the broadcasting signal will consume a considerable length of time thus increasing the overall duration of the full-range scanning process.
So far in 2001, the ground television signals of the U.S.A. broadcast system are provided in both analog and digital forms while the cable television signals are provided mainly in an analog form. It is hence desired to develop an improved TV receiver which is capable of receiving both a ground wave and a cable wave of the broadcasting signal and both an analog form and a digital form of the ground wave signal while is increased in the speed of full-range scanning process. This requirement will hardly be achieved by the teachings of the above Publication Nos. HEI 10-233970 and 2000-312134.